Cell cooling

ABSTRACT

To cool a semi-conductor cell a cryogenic arrangement is provided that gives a two-phase cooling in that, upon initiation of the cooling process, a refrigerant liquid reservoir supplies refrigerant liquid into a cooling chamber, where the liquid commences to boil, and then at the end of the first phase a refrigerant valve cuts off the supply of liquid refrigerant to the cooling chamber, an air valve opens to admit a flow of air to the cooling chamber to promote the boiling and simultaneously a vent valve opens to allow vapour to escape from the cooling chamber. The air entering the cooling chamber first passes through a heat exchanger in which it is cooled by heat exchange with a portion of the refrigerant.

Harding et al.

[ CELL COOLING [75] Inventors: Richard John Arthur Harding, St.

Albans; Colin Roy Moss, North Mimms, both of England [73] Assignee: Hawker Siddeley Dynamics Ltd.,

England [22] Filed: Apr. 25, 1967 [21] Appl. No.: 635,953

[30] Foreign Application Priority Data Apr. 29, 1966 United Kingdom 19071/66 [52] US. Cl. 102/70.2 R; 62/514 [51] Int. Cl. F42C 11/00; F25B 19/00 [58] Field of Search 62/514; 178/71; 102/702 [56] References Cited UNITED STATES PATENTS 3,314,473 4/1967 Smith et al 62/514 3315478 4/1967 Walsh et al. 62/514 [45] Aug. 19, 1975 3,372,556 3/1968 Waldman 62/514 Primary ExaminerStephen C. Bentley Assistant ExaminerC. T. Jordan Attorney, Agent, or FirmDowell and Dowell 5 7 ABSTRACT To cool a semi-conductor cell a cryogenic arrangement is provided that gives a two-phase cooling in that, upon initiation of the cooling process, a refrigerant liquid reservoir supplies refrigerant liquid into a cooling chamber, where the liquid commences to boil, and then at the end of the first phase a refrigerant valve cuts off the supply of liquid refrigerant to the cooling chamber, an air valve opens to admit a flow of air to the cooling chamber to promote the boiling and simultaneously a vent valve opens to allow vapour to escape from the cooling chamber. The air entering the cooling chamber first passes through a heat exchanger in which it is cooled by heat exchange with a portion of the refrigerant.

10 Claims, 5 Drawing Figures PATENTED AUG E 91975 SHEET 1 [1F 3 CELL COOLING DESCRIPTION OF INVENTION This invention relates to the rapid cooling of small masses to a low temperature. More particularly, the invention is concerned with increasing the sensitivity of semi-conductor cells by refrigeration.

The invention will be described in its application to proximity fuzes for missle warheads although it is not limited to this employment. Missiles that have warheads intended to explode automatically on passing close to a target may be fitted with fuzes in which the essential operative element is a semi-conductor cell sensitive to infra red radiations from the target. Such cells are not normally sufficiently sensitive but are made so at the appropriate time by cooling to a temperature below, say, 30C. This, indeed, constitutes the arming of the warhead.

The advantage in increasing the sensitivity of the cell as much as practicable is that it likewise increases the miss distance from the target at which the missile will still explode. At the same time, since active refrigeration of the cell is ordinarily only maintained for a comparatively short period, the desired situation is that arming, i.e. refrigeration of the cell, shall not commence until the missile is approaching the target and shall then occur as rapidly as possible, while measures to prolong the period during which the cell is kept at the low temperature, after initial refrigeration, are beneficial. Accordingly, the invention seeks to provide a means of cooling a semi-conductor cell very quickly to a low temperature, generally lower than has been attained hitherto, without creating noise" signals during the missile armed flight period such as might set off the warhead, and of delaying to some extent the time when the cell temperature rises after active refrigeration has ceased.

The previously employed way of cooling semiconductor cell in a fuze has been by releasing liquid refrigerant at the appropriate time and allowing it to boil off. According to the present invention, apparatus for the rapid cooling of a small mass, such as a semiconductor cell in a fuze, comprises means for releasing a liquid refrigerant at a selected time into a chamber from which it can boil off, the chamber being so situated in relation to the mass to be cooled that the mass partakes of the temperature reduction thereby resulting, and means for introducing a gas stream into the chamber to promote evaporation of the refrigerant and thereby reduce the temperature below the free boiling refrigerant temperature.

There may also be a porous heat sink, for example of sintered metal, situated around the cooled region thereby to enhance the cooling and retard the return of heat to the cell after active refrigeration has ceased.

In the preferred scheme, the refrigerant liquid is released first and then a few seconds later an air flow commences and simultaneously a vent opens to allow the refrigerant vapour in the chamber to flow to exhaust; the incoming air may be cooled by heat exchange with a small proportion of the refrigerant diverted into a heat exchanger for the purpose.

Ways of carrying the invention into effect will now be described by way of example with reference to the accompanying diagrammatic drawings, in which:

FIG. 1 shows in longitudinal section a fuze cell according to the invention,

FIG. 2 is a view in the direction of the arrow 2 of FIG.

FIG. 3 is a diagram of the refrigerant and air supply system for the cell,

FIG. 4 is a diagram to illustrate the operation of the cell, and

FIG. 5 is a diagram, similar to that of FIG. 4, illustrating a modification of the device.

FIGS. 1 and 2 illustrate a fuze cell according to the invention. A vented brass shroud 11 has an internal flange 12 against which is fitted a heat-insulating ring 13 which provides a seating for a copper plate 14. On its front face the plate 14 carries the semi-conductor cell 15 which may be of the type having an indium/antimonide sensitive patch 16 deposited on a Sintox ceramic substrate 17. Leads 18 for the cell are taken out through the shroud l1, and the cell faces out through a sapphire window 19 that is fitted at one end of the shroud by means of a bezel ring 20.

At the back of the copperplate 14 the region immediately opposite the cell patch 16 is enclosed by a generally frusto-conical porous thick-walled member 21 of sintered bronze which constitutes a heat sink. Conduits for refrigerant and air enter the interior of the coned heat sink 21 by way of a heat-insulating bush 22 that closes one end of the chamber 23 within the heat sink. A layer of felt 24 is placed around the outside of the heat sink 21 and the bush 22.

The conduits for supplying refrigerant and air comprise coaxial pipes, the inner pipe 25 bringing refrigerant liqiud in while the annular passage between the inner pipe 25 and the outer pipe 26 has air brought in through it. The inner pipe 25 projectsinto the chamber 23 beyond the outer pipe 26 and has end and side spray jets 27 for spraying the liquid refrigerant into the chamber. FIGS. 3 and 4 illustrate the arrangement in more detail. The inner pipe 25 is coupled to a liquid refrigerant reservoir 28 (FIG. 3) via a pipe 29 and an electrically-controlled valve 30. The reservoir 28 also has a vent 31 with an electrically-controlled valve 32. The air supply is derived from a high pressure air reservoir 33 via a pressure-reducing restriction 34, an electricallycontrolled valve 35 and a pipe 36. Air delivery from the pipe 36 takes place through a heat exchange coil 37 extending helically within the passage 38 between the inner and outer cell pipes 25, 26. Within the chamber 23 the end of the passage 38 around the coil 37 is blocked as at 39. The air entering through the coil 37 is in heat exchange relationship with outgoing refrigerant liquid in the passage, 38, the source of this liquid being an expansion orifice 40 in the side of the inner pipe 25 near the blocked end of the passage 38.

In a typical case, the refrigerant is Arcton 22 and flows alone into the chamber 23 thorugh the pipe 25 and sprays 27 for 3 seconds after the initiation of arming, ie after opening of the valve 30. Then the air valve 35 opens and simultaneously the refrigerant vent valve 32 opens. Air enters the fuze cell chamber through the already cooled heat exchange coil and the temperature of the air on entry to the cell cooler is in the range 30C to 40C. The air flows into the porous heat sink 21 and also to the felt 24, which have both previously been permeated by the refrigerant. The resulting increased evaporation of the refrigerant enhances the cooling effect by inducing supercooling which reduces the temperature of the heat sink and thus by conduction, the cell to the range 40C to 60C depending on ambient temperature conditions. This builds up a cold barrier around the chamber 23 which delays subsequent rise in its temperature. The air supply is sufficient for seconds flow.

The missile is armed 5 seconds after commencement of the flow of refrigerant, whereafter undue noise signals produced by the operation of the cell cooling system might set off the warhead. The venting of the refrigerant at 3 seconds helps to minimise the noise of the refrigerant boiling during armed flight. The armed flight time of the missile is, up to 60 seconds from the initiation of cooling, and the heat sink arrangement enables the cell temperatures to be held at a low level throughout that time.

Initiation of fuze cell cooling can be by means of a detonator exploding at a predetermined interval after lauching the missile, the circuitry incorporating a time delay switch to prevent premature arming of the warhead. In some instances, it may be advantageous for the time between launching and arming to be selectable in flight; the missile could be arranged for arming in response to a signal pulse transmitted at will by, in the case of an air-to-air missile, the launching aircraft.

Modifications of the arrangement described, are, of course possible without departing from the scope of the invention. Thus, the refrigerant and air could be delivered into the fuze cell through two pipes side by side instead of coaxial. And the semi-conductor itself may comprise more than one sensitive patch, with a corresponding increase in the area of the copper plate carrying it to be: cooled. 1

If desired, refrigerant can be vented from the supply system via the heat exchanger instead of direct to the atmosphere, thereby giving continued cooling during the air flow periodafter the refrigerant inflow has ceased. Suchan arrangement is illustrated in FIG. 5. An extra pipe 41 is connected between the refrigerant supply pipe 29 and a small orifice 42 in the outer wall of the'pipe 26 near the lower end thereof. The expansion orifice 40 is not now needed since the extra pipe 41 and the orifice 42 now provide the refrigerant supply to the heat exchanger. Operation during the first three seconds is as before. At the end of three seconds an electrically-operated piston valve 43 moves to the position shown in broken lines at 44 thereby cutting off the supply of refrigerant to the pipe and opening that pipe to atmosphere, while allowing the refrigerant in the supply system to continue to vent to atmosphere through the heat exchanger passage 38. The valvecontrolled vent 31 of FIG. 3 is in this case omitted.

We claim:

1. Apparatus for the rapid two-phase cooling of a small mass, such as a semi-conductor cell in a fuse, comprising a boil-off chamber so arranged in relation to the mass to be cooled that the mass will partake of a temperature reduction in said chamber, a normally sealed reservoir containing liquid refrigerant, a supply passage extending between said reservoir and said chamber, a separate source of gas under pressure, means operable to release liquid from said reservoir through said supply passage into said boil-off chamber at a selected time, and means conducting gas from said gas source into said boil-off chamber a predetermined time period after said release of liquid refrigerant to promote the evaporation of the refrigerant liquid and thereby reduce the temperature below the free boiling refrigerant temperature.

2. Apparatus according to claim 1, and comprising a porous heat sink surrounding the boil-off chamber.

3. Apparatus according to claim 1, further comprising normally closed vent means communicating with said chamber, and vent-operating means opening said vent a predetermined time period after said release of liquid refrigerant to allow the vapour in said chamber to flow to exhaust.

4. Apparatus according to claim 1, further comprising a heat exchanger wherein the entering gas flow is cooled by means of a proportion of the refrigerant diverted into said heat exchanger for this purpose.

5. Apparatus according to claim 3, comprising a refrigerant supply control valve, a gas supply control valve and a vent valve, and wherein closing of said refrigerant supply valve occurs simultaneously with opening of said gas supply and vent valves.

6. Apparatus according to claim 4, comprising valve means operative when the gas flow commences to shut off the flow of refrigerant liquid into said chamber while allowing refrigerant to continue to flow thereafter through the heat exchanger.

7. Apparatus according to claim 2, wherein said heat sink comprises an open-ended hollow member which defines within itself the aforesaid chamber, and the mass to be cooled is situated across one end of said hollow member while the other end affords entry for pipes or conduits conveying the refrigerant liquid and an air supply.

8. Apparatus according to claim 2, wherein the mass to be cooled comprises a semi-conductor cell sensitive to infra-red radiation, and a vented housing contains the heat sink and the cell which housing is fitted at one end with a window through which external infra-red radiation can reach the cell.

9. Apparatus according to claim 4, wherein a tube having spray jets at its end supplies the refrigerant liquid to said chamber, and the heat exchanger comprises an outer pipe surrounding the refrigerant supply tube and a tube coil extending within the space between the refrigerant supply tube and the outer pipe, the gas supply to the chamber passing through said coil.

10. Apparatus according to claim 9, comprising an expansion orifice through which the portion of the refrigerant which is diverted to cool the air supply enters the space around the heat exchanger coil. 

1. Apparatus for the rapid two-phase cooling of a small mass, such as a semi-conductor cell in a fuse, comprising a boil-off chamber so arranged in relation to the mass to be cooled that the mass will partake of a temperature reduction in said chamber, a normally sealed reservoir containing liquid refrigerant, a supply passage extending between said reservoir and said chamber, a separate source of gas under pressure, means operable to release liquid from said reservoir through said supply passage into said boil-off chamber at a selected time, and means conducting gas from said gas source into said boil-off chamber a predetermined time period after said release of liquid refrigerant to promote the evaporation of the refrigerant liquid and thereby reduce the temperature below the free boiling refrigerant temperature.
 2. Apparatus according to claim 1, and comprising a porous heat sink surrounding the boil-off chamber.
 3. Apparatus according to claim 1, further comprising normally closed vent means communicating with said chamber, and vent-operating means opening said vent a predetermined time period after said release of liquid refrigerAnt to allow the vapour in said chamber to flow to exhaust.
 4. Apparatus according to claim 1, further comprising a heat exchanger wherein the entering gas flow is cooled by means of a proportion of the refrigerant diverted into said heat exchanger for this purpose.
 5. Apparatus according to claim 3, comprising a refrigerant supply control valve, a gas supply control valve and a vent valve, and wherein closing of said refrigerant supply valve occurs simultaneously with opening of said gas supply and vent valves.
 6. Apparatus according to claim 4, comprising valve means operative when the gas flow commences to shut off the flow of refrigerant liquid into said chamber while allowing refrigerant to continue to flow thereafter through the heat exchanger.
 7. Apparatus according to claim 2, wherein said heat sink comprises an open-ended hollow member which defines within itself the aforesaid chamber, and the mass to be cooled is situated across one end of said hollow member while the other end affords entry for pipes or conduits conveying the refrigerant liquid and an air supply.
 8. Apparatus according to claim 2, wherein the mass to be cooled comprises a semi-conductor cell sensitive to infra-red radiation, and a vented housing contains the heat sink and the cell which housing is fitted at one end with a window through which external infra-red radiation can reach the cell.
 9. Apparatus according to claim 4, wherein a tube having spray jets at its end supplies the refrigerant liquid to said chamber, and the heat exchanger comprises an outer pipe surrounding the refrigerant supply tube and a tube coil extending within the space between the refrigerant supply tube and the outer pipe, the gas supply to the chamber passing through said coil.
 10. Apparatus according to claim 9, comprising an expansion orifice through which the portion of the refrigerant which is diverted to cool the air supply enters the space around the heat exchanger coil. 